A flow rate control device is used to adjust the flow rate of fluids such liquid chemicals in semiconductor manufacturing devices, and is also employed in the pharmaceutical and chemical fields when mixing liquids in desired ratios.
In this type of flow rate control device, it is known to arrange an orifice on the downstream side of a regulator. With this flow rate control device, the flow rate of a fluid is controlled by controlling the primary pressure of the orifice (i.e., the secondary pressure of the regulator) by means of the regulator (see for example Patent Reference 1).
However, with the flow rate control device, when one attempts to control the flow rate with a high degree of precision, it will be necessary to employ an orifice having a small opening, and thus the range of flow rates that can be controlled is narrow. In contrast, when one attempts to control the flow rate across a wide range, it will be difficult to control the flow rate with good precision because an orifice with a large opening will be employed. Thus, there is a problem with the flow rate control device, in that it cannot be used to both control the flow rate in a wide range and control the flow rate with a high degree of precision.
Accordingly, a device that can solve the aforementioned problem has been proposed, in which the valve opening of the orifice is adjusted by means of a motor (see for example Patent Reference 2). According to this technology, because the valve opening of the orifice is adjusted by means of a motor, the flow rate can be controlled in a wide range by setting the valve opening large, and the flow rate can be controlled with a high degree of precision by setting the valve opening small.
[Patent Reference 1] U.S. Pat. No. 3,623,125
[Patent Reference 2] U.S. Pat. No. 3,801,570